Want to make sure you attract a certain bird to your nest box Choose which birds occupy your bird box with these Silver Bird Box Cover Plates from Green Feathers. With entrance holes 25mm, 28mm and 32mm in diameters, these plates provide a strong seal around the entrance to prevent predators, such as woodpeckers, from gaining entrance and harming the nesting birds. Made from stainless steel, these plates in silver are guaranteed years of use.